PROJECT SUMMARY/ABSTRACT The immune system?s role in protecting the host from influenza virus infection has been extensively studied; however, leukocyte interactions with tissue-resident stem cells and extracellular matrix (ECM) components are increasingly being realized as essential for mediating tissue homeostasis and recovery. While recent single-cell RNA sequencing applications have allowed researchers to observe dynamic changes in gene expression profiles of individual tissue cell types throughout the course of the infection, how these cells spatially network to enact complex processes such as tissue repair remains poorly understood. As a demonstrative example of this gap in understanding, conditional deletion of a crucial repair-related growth factor, amphiregulin (Areg), in T cells impairs recovery after challenge with influenza virus. In light of the relatively small number of T cells among all lung-resident amphiregulin-producing cells, their overall significance is rather striking ? in addition to several other leukocyte-derived sources of Areg, lung epithelial and mesenchymal cells have also been shown to produce this growth factor during respiratory infections and in similar pathologic settings. Reconciling the massive presence of Areg during repair with the non-redundant roles of Areg from distinct low-frequency cell types necessitates further appraisal of the cell-to-cell interactions that dictate such processes. The major goals of this project are to: (1) characterize the role of Areg?s heparin-binding domain for mediating recovery from influenza virus infection, (2) assess the relative influence of deposited and/or cell surface?localized heparan sulfate proteoglycans in spatially defining T cell?derived Areg signaling, and (3) determine how these tissue processes dictate susceptibility to severe influenza outcomes. Successful completion of this proposal?s objectives will provide a greater understanding of T cell?derived factors that mediate protection against influenza virus and potentially impact our comprehension of immune mechanisms that contribute to severe disease.